[jeffbee]

On my local system md5sum takes 1.9 user CPU-seconds per GB.

  $ time dd if=/dev/zero bs=1048576 count=1024 | md5sum
  1024+0 records in
  1024+0 records out
  1073741824 bytes (1.1 GB, 1.0 GiB) copied, 2.104 s, 510 MB/s
  cd573cfaace07e7949bc0c46028904ff  -

  real    0m2.108s
  user    0m1.891s
  sys     0m0.628s

[JdeBP]

If you want to try measuring something more relevant, my redo implementation comes with a cubehash tool that uses the same hash as redo-ifchange et al. do.

* http://jdebp.uk./Softwares/redo/

[tyingq]

Can you try cksum instead?

[jeffbee]

3.3s here. Is it faster on your system?

[tyingq]

No, was hoping a non-cryptographic checksum would be faster. Perhaps cksum isn't the one.

Edit: "sum -s" is faster for me, but the man page doesn't give much info on what the algorithm is.

[jeffbee]

Well it returns 00000 for /dev/zero so it looks like it is a quite useless 16-bit check.